1. Field of the Invention
The present invention is related generally to a method for dry-cleaning garments or fabrics, and, more particularly, to such method using gas jets to provide agitation that removes insoluble/particulate soils and prevents the re-deposition of such soils.
2. Description of Related Art
A typical dry-cleaning process consists of a wash, rinse, and drying cycle with solvent recovery. The garments are loaded into the cleaning drum and immersed in cleaning fluid pumped into the drum from a base tank. The soluble soils associated with the garment fabrics dissolve in the cleaning fluid and hence are readily removed. However, insoluble soils must be physically dislodged from the fabrics by agitation. Accordingly, the drum tumbles the garments during the wash and rinse cycles to provide the necessary agitation to remove insoluble soil by physical dislodgment.
Sufficient care must be exercised to prevent the re-deposition of insoluble soil (also termed "particulate soil") on the garments once it is initially removed. Generally, once a soil has re-deposited onto a garment, it cannot be removed by subsequent agitation. Accordingly, high solvent flow rates (on the order of one gallon per minute per pound of garments) are generated to transport solvent-containing particulate soil out of the cleaning chamber and through a battery of filters before soil re-deposition occurs. At regular intervals, the cleaning fluid must undergo a distillation step to remove the dissolved soils and dyes. The stills are either part of the dry-cleaning machine itself, or self-standing.
The dry-cleaning industry has employed such solvents as perchloroethylene (PCE), petroleum-based or Stoddard solvents, CFC-113, and 1, 1 ,1-trichloroethane, all of which are generally aided by a detergent. However, an application having the same assignee as the present application (Ser. No. 08/236,776; filed Apr. 29, 1994; entitled "Dry-Cleaning of Garments Using Liquid Carbon Dioxide Under Agitation as Cleaning Medium") discloses an apparatus and method for employing liquid carbon dioxide as the cleaning medium in dry-cleaning operations. The contents of that application, hereinafter referred to as the "Liquid Carbon Dioxide" application for brevity, are incorporated herein as a reference.
Regardless of the type of solvent used, agitation of garments in the cleaning medium is performed to accelerate removal of soluble soils and is essential in the removal of particulate (insoluble) soils. When conventional dry cleaning solvents are used, agitation is generally supplied by a rotating drum as described above. When liquid carbon dioxide is used, agitation may be provided by several means, such as gas bubble/boiling processes, liquid agitation, sonic agitation, and liquid agitation by stirring. Each of these agitation processes are described in the above-mentioned related "Liquid Carbon Dioxide" application. In short, the gas bubble/boiling processes induce agitation by boiling the cleaning solution so that gas bubbles are produced which, in turn, initiate the garment agitation and tumbling necessary for particulate soil dislodging. Liquid agitation involves providing liquid solvent inflow through one or more nozzles arranged in such a configuration as to promote the tumbling action through agitation of the cleaning medium and thus the garments contained therewithin. Sonic agitation involves agitating the garments and fabrics with pressure waves and cavitation using sonic nozzles strategically placed around the internal perforated garment basket. Finally, liquid agitation may be provided by simply stirring the cleaning solvent with the use of, for instance, an impeller located under the mesh garment basket. It is also known to use various agitation methods simultaneously to achieve greater agitation.
It follows that, given the various types of equipment and chemicals employed in the dry-cleaning trade, it is relatively expensive to set up and operate a dry-cleaning establishment. The initial capital investment includes the purchase of a costly cleaning chamber with an agitation means as well as expensive pumps and large diameter plumbing, which is required to generate the high solvent flow rates used to prevent particulate soil re-deposition. Operating expenses include high electricity costs to drive pumps generating high solvent flow rates, as well as the cost of cleaning solvents.
While the expense of cleaning solvents is reduced with the use of such dense phase gases as liquid carbon dioxide as opposed to conventional cleaning solvents, the initial capital equipment costs are even more pronounced in dry-cleaning processes utilizing dense phase gases. The higher costs stem from the necessity of operating such systems at high pressure in order to maintain the gases in a liquid state. For example, the operating pressure of a cleaning chamber employing liquid carbon dioxide ranges from about 500 to 1,500 psi (pounds per square inch; 35.2 to 105.4 Kg/cm.sup.2) for the purpose of maintaining the carbon dioxide in a liquid state. The cost of high pressure chambers increases linearly with pressure, height, and the square of their radius. Thus, while liquid carbon dioxide costs only a fraction of the cost of conventional dry-cleaning solvents (such as PCE) and is preferred in terms of its environmental soundness, the higher initial capital investment required to implement a liquid carbon dioxide dry-cleaning operation may prohibit a transition from conventional dry-cleaning solvents.
Thus, there is a need for a method of dry-cleaning that provides the agitation necessary for removal of insoluble soils that is more cost-effective than existing equipment.